The story of a man who ended up needing a liver transplant after taking green tea capsules has brought the topic of dietary supplements back into the news. What are some of the dangers of supplements and what are the health benefits?

When Jim McCants started taking green tea pills he had hoped he was giving his health a shot in the arm.

Instead, it appears the pills caused such serious damage to his liver that it required an urgent transplant.

Experts point out that experiences like that of Mr McCants, are "extremely unusual".

In the UK, supplements are subject to EU regulations over their safety and the health claims manufacturers make about the products.

Approved supplements bought from reputable businesses are almost always going to be safe, provided the manufacturer's instructions are followed, doctors say.

But it is wrong to assume that food supplements do not sometimes have the potential to be harmful, says Dr Wayne Carter, from the University of Nottingham.

If you take supplements in quantities above recommended levels there are risks.

While in many cases excess levels of a supplement will be excreted, there is the potential for it to be toxic, particularly to the liver, which detoxifies the substances we consume.

"I think sometimes the idea that people take on board is 'this is good for me, therefore if I take even more of it, it will be even better'," Dr Carter says.

"This isn't without risk."

There is also a potential danger in indiscriminately taking many supplements at the same time, says Dr Carter.

Sometimes they can interact with one another - that is, one supplement may strengthen the effects of another - while in other cases they might contain one or more of the same nutrients, potentially leading to excess levels.

Some of us may be less able to metabolise certain substances effectively, which can also influence how they affect us.

"The caveat with taking a supplement is it could be safe in a broad population, but not in everyone," Dr Carter adds.

But if these are some of the potential risks, what are the health benefits?
Supplements for child health

There are some supplements that are widely acknowledged by experts to be of benefit across the population.

The NHS recommends that women who are thinking of having a baby should have a folic acid supplement, as should any pregnant woman up to week 12 of her pregnancy, to prevent common birth defects in babies.

The government this week said it would consult on adding folic acid to flour, following repeated calls for the move from experts.

Vitamin D supplements are also recommended in babies, children between the ages of one and four, and people who are not often exposed to the sun.

This includes those who are frail or housebound or usually wear clothes that cover up most of their skin when outdoors.

The rest of the population is advised to consider taking a Vitamin D supplement.